Technical Field
The instant disclosure relates to an auto focus method and an apparatus using the same, and particularly relates to an auto focus method and an apparatus using the same in which auto exposure and auto focus functions are performed at the same time.
Related Art
One of the auto focus (AF) methods for image capturing apparatus is the contrast focus method. In the contrast focus method, the lens of the image capturing apparatus is moved, an image is obtained at each of the stepping positions, and contrast values of the obtained images are calculated. And then, the image capturing apparatus compares all the contrast values and taking the stepping position corresponding to the maximum contrast value as the focal point. The image capturing apparatus further has an auto exposure (AE) function. In the auto exposure function, the aperture and the shutter of the image capturing apparatus are adjusted according to the environmental brightness and preset output brightness during the image capturing apparatus obtains images, and the adjustments of the aperture and the shutter will change the amount of incident lights into the lens. Accordingly, the images obtained by the image capturing apparatus have a uniform brightness.
However, during the image capturing apparatus performs auto focus function, if the image capturing apparatus also performs the auto exposure function at the same time, the exposure values of the obtained images would be affected in response to the adjustments of the aperture and the shutter. Therefore, the brightness of the obtained images is changed and the contrast values of the obtained images are affected accordingly. Hence, an error would be generated in determining the values of the contrast values.
Accordingly, the image capturing apparatus would mis-determine the focal point.
To solve the aforementioned problems, a conventional approach is to lock the auto exposure function during the image capturing apparatus performs the auto focus function, and the auto exposure function can be launched until the focal point is founded. However, during the image capturing apparatus performs the auto focus function, if the obtained images are overexposure or underexposure, the image capturing apparatus is unable to perform the auto focus function due to the auto exposure function is locked, and consequently the user may feel the response time of the auto exposure function is too long. On the other hand, if the auto focus function is activated after the completion of the auto exposure function, the user may feel the response time of the auto focus function is too long.